1. Field of the Invention
This invention relates generally to monitoring of usage of aircraft parts, systems and functions, and more particularly concerns monitoring of aircraft braking systems.
2. Description of Related Art
Automatic braking systems have been commonly provided on commercial aircraft to aid the deceleration of the aircraft upon landing. As the size and complexity of aircraft have increased, the automatic braking systems have also become more complex and computerized. Modem anti-skid systems incorporated into aircraft braking systems commonly optimize braking efficiency by adapting to runway conditions and other factors which affect braking in order to optimize deceleration, typically corresponding to the level of brake pressure selected by the pilot.
In a conventional skid detection system used in aircraft braking systems typically includes a wheel speed transducer for each wheel brake of the wheels of the aircraft, for measuring wheel speed and generating wheel speed signals that are a function of the rotational speed of the brake wheel. The wheel speed signal is typically converted to a signal representing the velocity of the aircraft, and compared with a desired reference velocity, to generate wheel velocity error signals indicative of the difference between the wheel velocity signals from each braked wheel and the reference velocity signal for providing anti-skid control of aircraft braking.
Aircraft brakes often constitute the most expensive single maintenance item to the airlines, because they wear out and are expensive to replace. The demands on aircraft brakes are extraordinary due to the high speeds at which aircraft braking typically occurs, causing aircraft brakes to periodically wear out and require replacement. In emergency braking situations, reverse thrust may not be available, high performance engines can take several seconds to reduce thrust, and flight control surfaces may be able to generate little aerodynamic drag, placing the burden of slowing the aircraft almost completely on the aircraft braking system. In such situations, although the aircraft wheel size maybe comparable to that of an average car, the amount of energy that must be absorbed per brake can be equivalent to what a car brake would absorb completely stopping an average car from a speed of 60 miles an hour 200 times.
Aircraft brakes are typically have a brake stack formed of multiple disks, in which the key elements are the rotors and stators which absorb the energy of a stop. The rotors are keyed to and rotate along with the wheels, while the stators, tied to the axle, are stationary. Hydraulically operated brake pistons compress the rotors and stators together to provide the frictional forces necessary to brake an aircraft. One or more metal wear pins are attached to the pressure plate, or first stator, of a brake stack, and extend through a hole in the brake""s actuator housing. When the brake is new, the pins extend past the housing by some amount (e.g. one or two inches). As the brake wears, the pressure plate moves away from the brake actuator housing, and the wear pins move with the pressure plates. The stroke of the brake pistons is automatically adjusted by brake actuator adjusters based upon the brake wear indicated by the wear pins, so that when the brakes are released, the actuators only retract a fixed small amount, independent of brake wear.
Aircraft brakes are commonly guaranteed for a given number of landings, and the number of landings is commonly used as the overall measure of brake usage. However, the rate at which aircraft brakes wear and require replacement, and hence the cost of maintenance of aircraft brakes, is heavily dependent upon how such aircraft brakes are used. Factors such as aircraft wheel speed and brake pressure, as well as how an operator applies brakes during each flight cycle can greatly affect aircraft brake wear. There thus remains a need for an improvement in the monitoring of aircraft brake usage. Improved aircraft brake usage monitoring would provide a better basis for guaranteeing brakes, and would provide valuable data to help the airline operator improve landing and braking procedures to achieve lower brake costs. The present invention meets these needs.
Briefly, and in general terms, the present invention provides for a system and method for monitoring aircraft braking system usage that can reduce aircraft operating costs by providing data which may be used to better guide operating and maintenance procedures. The present invention provides for continuous monitoring of brake wear, and stores one or more key parameters affecting brake wear for periodic access by ground personnel. The brake usage data will provide a more accurate basis for guaranteeing the life of aircraft brakes, determining when aircraft brakes need to be replaced, and will provide data for improving pilot landing and braking techniques to achieve better brake economics.
The present invention accordingly provides for a system and method for monitoring wear of one or more aircraft parts. In a presently preferred embodiment, an aircraft brake is monitored for wear, although the invention can also apply to monitoring of wear of other aircraft parts, such as an aircraft tire, a standby system, landing gear, and the like. In the system and method of the invention, one or more sensors are provided for sensing a parameter of usage of the one or more aircraft parts and for generating a signal indicating a sensed value of the parameter of usage of the aircraft part. An estimate of usage of the part is determined based upon the signal indicating the sensed value of the parameter of usage of the aircraft part. In one preferred aspect, the estimate of usage of the part is stored for access of the estimate by ground personnel. In another preferred aspect, the one or more sensors for sensing a parameter comprises a plurality of sensors for sensing usage of a plurality of parts of the aircraft, and the means for determining an estimate of usage comprises a central computer.
In a presently preferred embodiment, an aircraft brake is monitored for wear, and the one or more sensors comprise a linear brake wear indicator attached to the brake. Each time the brake is actuated, the linear brake wear indicator moves a discrete distance, and a linear position encoder is provided for measuring and generating a linear position signal indicating the distance travelled by the linear brake wear indicator as an indication of brake usage. An estimate of brake usage is determined based upon the distance travelled by the linear brake wear indicator as indicated by linear position signal.
In one presently preferred embodiment, as applied to monitoring wear of an aircraft brake, a wheel speed monitor is provided for generating a wheel speed signal indicating wheel speed of the aircraft, and the means for determining an estimate of usage receives the wheel speed signal for distinguishing between static brake applications and moving brake applications, based upon the wheel speed signal. In another currently preferred aspect, means are provided for measuring the period of time elapsed during each brake application, and the distance over which each brake application occurs is determined based upon the wheel speed during each brake application and the period of time elapsed during each brake application, in order to determine the degree to which each individual brake application contributes to brake wear.
In another currently preferred embodiment, as applied to monitoring wear of an aircraft brake, a temperature sensor is provided for sensing brake temperature, and for generating a temperature signal indicating brake temperature that is received by the means for determining an estimate of usage. The estimate of brake usage can be determined based upon the input of the temperature signal. In another presently preferred aspect, the degree to which each individual brake application contributes to wear can be estimated based upon the temperature signal.
In another presently preferred embodiment, as applied to monitoring wear of an aircraft tire, a wheel speed monitor is provided for generating a wheel speed signal indicating wheel speed of the aircraft, and the wheel speed signal can be used for distinguishing between static brake applications and moving brake applications based upon the wheel speed signal, and for determining an estimate of tire usage. A sensor is also preferably provided for sensing aircraft yaw, and for generating a yaw signal indicating aircraft yaw, that can be used for determining an estimate of tire wear based upon the wheel speed signal and the yaw signal.
In another presently preferred embodiment, when the aircraft part to be monitored is a standby system, a sensor is provided for sensing input power to the standby system and for generating an input power signal used for determining an estimate of usage. Means are also preferably provided for measuring the period of time elapsed during each usage of the standby system and for generating an elapsed time signal for determining an estimate of usage of the standby system based upon the input power signal and the elapsed time signal.
In another presently preferred embodiment, when the aircraft part to be monitored is a landing gear, a sensor is provided for sensing load on the landing gear and for generating a load signal for determining an estimate of usage of the landing gear. Means are also preferably provided for measuring the period of time elapsed during each usage of the landing gear and for generating an elapsed time signal for determining an estimate of usage of the landing gear based upon the load signal and the elapsed time signal.
These and other aspects and advantages of the invention will become apparent from the following detailed description and the accompanying drawings, which illustrate byway of example the features of the invention.